I think that the second season of Fringe is like a bridge between the 'Fringe-scientific topics' of the first and the more orthodox theories of the third, like relativity and quantum mechanics.

But if during the three seasons are cited some of the most famous names associated with these theories, from Einstein to Planck to Pauli, there's never ​​a reference to Erwin Schrödinger and his famous cat paradox.

Schrödinger's cat is a thought experiment which explains what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects. The experiment interpretation's implies that the cat remains both alive and dead (to the universe outside the box) until the box is opened.

Emblematic of the Observers' role, this theory introduces the concept that, in quantum mechanics, the observer is not only a bystander but integral part of the system.